Prior art devices for holding a book open are generally of such a large size and configuration that they are impractical for carrying in one's pocket for subsequent use. Examples of such devices appear in U.S. Pat. Nos. 1,196,715; 2,276,897 and 3,661,405.
Physically smaller prior art devices generally hold only the leaves on one side of the spine of a book and thus require two separate devices, one on each side of the spine of the book for keeping the desired pages in open position. They also require anchoring the device to the hard cover of the book and thus are difficult to use with paper back books. Examples of such devices appear in U.S. Pat. Nos. 1,150,678; 1,646,291 and 1,710,949.